An oxide semiconductor typified by amorphous IGZO (In—Ga—Zn—O) has a high carrier mobility, can be manufactured at room temperature, and has a large optical band gap (i.e., has transparency to visible light), and thus application of the oxide semiconductor to a thin-film transistor (hereinafter also referred to as a TFT) or the like, such as a driving element of an active-matrix display such as an organic electroluminescent (EL) display has been examined.
As a method of evaluating such an oxide semiconductor, conventionally, there has been a proposed technique of determining mobility using a microwave photoconductivity decay (μ-PCD) method (see Patent Literature (PTL) 1, for example).
With a microwave photoconductive decay method disclosed by PTL 1, a sample on which an oxide semiconductor thin film is formed is irradiated with excitation light and a microwave. After the maximum value of a reflected wave of a microwave from the oxide semiconductor thin film which is changed by the irradiation of the excitation light is measured, the irradiation of the excitation light is stopped. The change in reflectance of the reflected wave of the microwave from the oxide semiconductor thin film after the stop of the irradiation of the exciting light is measured. A lifetime value is calculated from the measured value, and thereby mobility of the oxide semiconductor thin film is determined. With the above-described technique, a non-contact evaluation and measurement of mobility of the oxide semiconductor thin film is implemented.